1. Field of the Invention
The present invention relates to an electric fan, preferably used in an electric vacuum cleaner and the like. The present invention relates also to an electric vacuum cleaner including an electric fan.
2. Description of Related Art
JP H9(1997)-14192A discloses an electric fan that includes an impeller rotated by a motor and is used in the above-mentioned technical fields. In this electric fan, when the total area of a virtual columnar face inside the impeller, formed by connecting center-side ends of a plurality of blades inside the impeller, is taken as S1, and the total area of an air inlet of the impeller is taken as S0, S1/S0 is set to 1.0 to 1.4. In a cross section including a rotational axis, when the radius of curvature in the vicinity of a central opening portion of a side plate of the impeller is taken as R, and the width of the center-side ends of the blades in the impeller in the direction of the rotational axis is taken as b, R/b is set to 0.6 to 0.9. It is stated that, with this configuration, air blowing efficiency can be kept high.
FIG. 16 is a partial cross-sectional view along a face including a rotational axis of an impeller 130 configuring the above-described conventional electric fan. When the impeller 130 rotates about a rotational axis 130a, a flow of air (air flow) 135 is formed that flows in from a central opening portion (air inlet) 132a of a side plate 132 and flows out from an air outlet 139 between a circumferential portion 132b of the side plate 132 and a circumferential portion 131b of a main plate 131.
However, as seen from FIG. 16, the conventional electric fan has a problem in that air blowing efficiency is lowered by a turbulent flow, referred to as a vortex flow 134, formed in the flow channel in the vicinity of the central opening portion 132a of the side plate 132.